Such solidified, erodible, aqueously based, airtreating gel reservoirs have had a long history of use as a means from which to deliver volatilizable air treating materials due to their economy, ease of manufacture and their effectiveness in gradually introducing those materials into the air for the purpose of creating a fragrance awareness.
However, this methodology is also accompanied by a number of disadvantages including a tendency for syneresis, unsightly appearance of the shrunken gel residue, uncontrolled and inefficient rates of release and large differences in size between a new and spent reservoir, resulting in an emanating surface which continually diminishes in size. Solid air treating gels are predominantly aqueous compositions and as such are characterized by a high degree of erodibility as evidenced by their large change in size as they become depleted overtime. Typically, units are on the order of 150-250 grams in weight and as a result, represent one of the larger sized options available in the area of continuous action sustained release fragrance methodologies. Depending upon such factors as air movement, humidity, and temperature, as well as the area of exposure set by the consumer, these units routinely last from three to six weeks. The physical change in size of the eroding reservoir typically results in a perceptible disparity in performance between newly opened units and those which might have been opened and exposed for only one week.
Originally, these types of gels were preformed into blocks or cast directly into vacuum-formed plastic containers. More recently, however, numerous types of container options have become available which encase the gel as well as offer some degree of control over the rate of release of the air treating components from the gel reservoir. Typically, such containers consist of two parts, a base and a cover housing which can either be raised or lowered to expose all or a desired portion of the gel reservoir. This configuration thus offers some influence over the rate of release of volatilizables from the unit. To this end, numerous modifications have been made not only in the options available in the gel composition, but also in the design of the dispenser. These improvements have all been directed at addressing some of the more significant shortcomings typically associated with this method of dispensing.
The use of gels and their long history of development can be seen in such prior art as U.S. Pat. No.2,466,146 (Baker) which details the use of a number of hydrocolloids for the purpose of preparing elastic gels.
U.S. Pat. No. 3,945,950 (Vosganiantz) describes the use of a substantial percentage of a volatilizable water-soluble glycol ether into the gel formulation in order to provide for a more regulated release from the solid gel composition.
U.S. Pat. No. 4,056,612 (Lin) details the development of air freshening gels which exhibit essentially no syneresis as well as improved gel strength through the use of an ammonium salt as part of the gel formulation.
U.S. Pat. No. 4,178,264 (Streit et al.) demonstrates the use of metallic stearates as a formulation enhancement for improving the thermal stability of carrageenan-based gel air freshening systems.
Similarly, the development of the dispenser for air treating gels also has shown a history of continual improvement.
U.S. Pat. Nos. 2,878,060 and 3,239,145 (Russo) demonstrate the use of a cylindrical and telescoping dispenser which provides a means of adjustability in combination with an integral seal which prevents the loss of vapor during periods of non use.
U.S. Pat. No. 3,908,906 (Crowe et al.) further develops an easily-fabricated loadable container which provides the option of adjustability with an integral sealing mechanism.
U.S. Pat. No. 3,910,495 (Cummings, et al.) details the development of an adjustable gel housing with a vapor-tight seal and the need for fewer operations in the molding of the container housing.
Air treating gels typically use a hydrocolloid as a gelling agent at concentrations ranging from 0.75% to 4% with an aqueous concentration which frequently approaches 90% in conjunction with an air treating component between 1% and 5%. In addition, the aqueous concentration of the gel formulation can contain co-solvents which provide increased solubility for the particular essential oils and fragrances dispersed within the aqueous medium. These co-solvents are typically used at a concentration of between 2% and 6% and are represented by such materials as propylene glycol, dipropylene glycol, hexylene glycol, dipropylene glycol methyl ether and ethanol or the like. It can easily be seen based on this composition that the co-evaporation of water with volatile air treating agents results in a reservoir with a high concentration of volatilizables and as such is accompanied by a high degree of shrinkage. The continued reduction in this reservoir size results in a smaller emanating surface and a diminished interface between this gel releasing surface and the surrounding atmosphere. This contributes to a reduction in the diffusion rate of the co-evaporants and a significant disparity in the performance of the unit as measured by its ability to create a fragrance awareness. Typically, these devices perform well when newly opened but noticeably decline in their effectiveness upon further use thereof. This limitation has frequently been cited as a major shortcoming of this technology and has been a primary reason why this delivery system has not found greater acceptability and application. As previously noted, the prior art has continued to improve the nature of the gel composition used in these reservoirs as well as to further develop the packaging. Little, however, has been done in the methodology to develop a device with a more consistent sustained effectiveness in the presence of a continually diminishing reservoir size.
My prior U.S. Pat. No. 4,809,912, in an effort to exert more influence over the rate of release of a gel dispensing system, details an alternative methodology and device to the above mentioned prior art. The unit of the '912 patent employs a rate controlling membrane disposed over the primary opening at the top of a gel container housing. During filling, heated and liquified air freshening gel is introduced through a fill hole at the bottom of an inverted container onto a porous covering membrane. The gel upon cooling, solidifies and becomes intimately attached to this membrane. The membrane provides support by which the emanating surface of the gel in contact with the membrane is kept dimensionally intact, such that the normal tendency of the gel to shrink inward is negated. The uniformity in the surface area of the emanating face of the gel in contact with the membrane contributes to a more uniform rate of diffusion throughout the functional life of the device.
In a similar effort to maintain a more dimensionally stable emanating surface, the dispenser of my U.S. Pat. No.5,060,858 uses a narrow absorbent band or some mechanical means of attachment that are positioned at the perimeter of the gel container adjacent its primary opening. Again, in a bottom fill procedure, heated liquified gel engages the absorbent band or the mechanical means at the top of the container, and upon cooling, that gel portion contacting the porous band or mechanical means becomes essentially fixed in place and immobilized. When a dispenser of the '858 patent is activated, the gel portion, which is anchored in place, is not permitted to shrink inward, whereas the gel beneath this segment continually shrinks from the bottom upward towards the emanating surface. Eventually, the entire reservoir moves upward and depletes itself leaving only a residue in the segment anchored to the container. The benefit of the '858 technology is once again the stabilization of the emanating surface such that it remains dimensionally unchanged and provides a more uniform fragrance transmission.
However, my attempts to improve the air treating performance, although providing a more controlled rate of release, require more packaging components and an increased number of assembly operations prior to filling. Accordingly, there is still a need for an improved air treating device, which stabilizes the emanating surface of the emanating face of the enclosed air treating gel, that is also structurally simple and relatively easy to manufacture.